Synergistic mechanisms of retigeric acid B and azoles against Candida albicans

Abstract

Aims: To clarify the underlying synergistic antifungal mechanisms of retigeric acid B (RAB) in combination with azoles against Candida albicans. Methods and Results: Increased accumulation of rhodamine 123 in C. albicans was measured by both spectrophotometric method and flow cytometry. The inhibitory properties to the drug efflux of C. albicans were determined spectrophotometrically. The decreased cellular ergosterol synthesis was measured using its unique spectrophotometric absorbance profile, and the downregulation expression levels of CDR1 and ERG11 were detected by real‐time reverse transcription polymerase chain reaction. Transmission electron microscopy investigation found the wrinkled cell membrane and the impaired cell wall. Conclusions: RAB synergizes the antifungal effect of azoles against C. albicans by inhibiting efflux pump activity, targeting the ergosterol biosynthesis pathway and increasing the fluidity for the resulted ergosterol depletion. Significance and Impact of the Study: Investigating the mechanism of the synergy between RAB and azoles against C. albicans will help us to uncover the antifungal roles of this lichen‐derived triterpene acid and find its possible clinical applications in overcoming fungal resistance.

Retigeric Acid B Enhances the Efficacy of Azoles Combating the Virulence and Biofilm Formation of <i>Candida albicans</i>

“…[22][23][24][25] Specifically, our previous study found RAB displayed a synergistic action with azoles against the growth of C. albicans. 11) In the study, we compared the effects of the RAB-azole combination treatment to mono-drug therapy on hyphae formation. Our results showed that the treatment with RAB-azoles combination blocked the yeast-to-hyphal transition in C. albicans in vitro, while cells under mono-drug therapy grew mainly in hyphae or pseudohyphae form (Fig.…”

“…Strains and Media C. albicans isolates YEM30, SC5314, CA2, 11) CA10 11) and CASA1 with green fluorescent protein (GFP) tagged CDR1 12) were used in this study and stored in culture medium supplemented with 10% (v/v) glycerol at −80°C. The isolates were propagated in YPD medium plates containing 2% agar at 30°C, inoculated into liquid YPD medium (2% tryptone, 1% yeast extract, 2% glucose) and incubated overnight in an orbital shaker (100 rpm) at 30°C.…”

“…The source of chemicals mentioned above and their preparations for the in vitro experiments have been reported in our previous paper. 11) For the therapy of infected mice, RAB and FLC were dissolved in a mixed solution containing 1,3-propanediol (20%), dimethyl sulfoxide (DMSO) (1%), Tween 80 (1%) and sterile physiological saline (78%).…”

“…11) To determine whether the same combination could inhibit the yeast-to-hyphal transition, C. albicans was treated with RAB and azoles alone or in combination. The cell morphotype was observed throughout 24 h and the percentage of hyphae formation at three hours was calculated in each treated group.…”

“…11) In the study we reported here, we sought to determine whether a synergistic effect could be observed between RAB and azoles to result in lowered virulence and reduced the biofilm formation of C. albicans.…”